Current approaches to evaluating and quantifying the risks of therapeutics, particularly after they are approved for marketing, clearly are insufficient. Given that all therapeutics represent a balance between the associated benefits and risk, improved risk-assessment methods are required in order to make informed regulatory and prescribing decisions. The Centers for Education & Research on Therapeutics (CERTs) therefore are planning a conference on risk assessment of marketed pharmaceuticals. The meeting is planned as a "think-tank" session and its primary goal will be to develop a research agenda to better understand how to quantify the risk of marketed drugs and biologicals. It is the second in a series of meetings that has the ultimate goal of defining a research agenda for management of the risks of medical products. This meeting should lead to publications and follow-up sessions that will improve both our base of knowledge and the quality of medical care, by improving the system for assessing the safety of therapeutic products. This Risk Series is being conducted under the aegis of the CERTs in collaboration with the Center for Drug Evaluation and Research (CDER) at the U.S. Food and Drug Administration (FDA), the Agency for Healthcare Research and Quality (AHRQ), and the Pharmaceutical Research and Manufacturers of Americal (PhRMA). The CERTs have the mission of conducting research and providing education that will advance the optimal use of drugs, medical devices, and biological products.